Study On The Sensing System Of Monitoring Cadmium In Oily Wastewater Based On A-GFET

In recent years,a lot of industrial wastewater and domestic sewage are discharged into the environment directly or indirectly due to the rapid development of industrialization,resulting in the problem of water pollution is becoming increasingly serious.It is worth noting that among the pollutants that cause water pollution,heavy metal ions are more threatening to human life and health.At present,the traditional ion detection methods include atomic fluorescence spectrometry（AFS）,atomic absorption spectrometry（AAS）,mass spectrometry and so on.Although these methods have advantages of high sensitivity and relatively reliable results,they are unable to meet the needs of rapid,simple and on-site detection due to the large volume of detection equipment and the need for sample pretreatment.The aptamer-graphene field effect transistor（A-GFET）biosensor has a broad application prospects in ion detection due to its high selectivity and rapid response.In this paper,based on the current research of A-GFET,we design a threshold sensor for cadmium ion detection to realize the real-time monitoring of the cadmium ion concentration in oil-bearing wastewater.The sensor will send out an alarm signal if the concentration of cadmium ion in the solution exceeds the set value.This dissertation analyzes the electrical characteristics of the graphene field effect transistor and explains the principle of sensing using the theory of electrostatic induction,charge conservation and double electric layer.And then,combined with the electrical characteristics and sensing principle,a mathematical model of the functional relationship between the cadmium ion concentration and the response signal is established.A-GFET is fabricated by Micro-Electro-Mechanical System（MEMS）technology.The process includes three parts:preparation of metal electrode,transfer and graphic processing of graphene and modification by PASE and aptamer.After modification by PASE and aptamer,the graphene is characterized by Raman spectroscopy and Energy Dispersive Spectrometer analysis（EDS）to ensure the successful modification of graphene.Then we use A-GFET sensor detect different concentrations of cadmium ions solution,fit the experimental data by mathematical model established previously and calculate the detection limit of the sensor.In addition Cr³⁺,Pb²⁺,Mg²⁺and Fe³⁺are used as control ions to test the selectivity of the sensor.The experimental results show that this sensor has good selectivity to cadmium ions.This work designs the circuit diagram and fabricates a PCB board according to the diagram to realize the acquisition and processing of data detected by A-GFET.The experimental results show that when the concentration of cadmium ion in the solution increases to a certain value,the circuit part will send out a photoacoustic alarm signal.In this paper,the preparation principle of superwetting surface is analyzed.superoleophobic/superhydrophilic isolation membrane is prepared by stainless steel mesh and FS-50,which is used to filter impurities and grease in oil-bearing wastewater,so as to ensure the detection performance of A-GFET.Finally,the cadmium ion concentration threshold sensor is constructed by combining the isolation membrane,A-GFET detection platform and PCB board.